Toyota Motor Sales U.S.A. Inc. reports its worst monthly sales decline in a year-long slump, with July deliveries off 18.7% from like-2007 on an adjusted basis.

It is the largest drop-off in Toyota’s monthly U.S. sales since October 2002, when it registered a 20.6% decline, Ward’s data shows.

Excluding October and November 2007 (at 0.5% and 0.3%, respectively), Toyota has not had a positive monthly sales result since June 2007.

Toyota Div. sales were off 17.6%, while the auto maker’s luxury Lexus Div. saw deliveries plunge 24.6%.

Passenger-car sales slumped 5.4% from July 2007, but it was Toyota-brand light trucks, down 34.3%, that accounted for the majority of the overall decline at Toyota Div.

While all the usual suspects, including the fullsize Tundra pickup truck, suffered hefty losses in July, Toyota’s two largest SUVs, the Sequoia and Land Cruiser, both redone for ’08, proved resilient, up 50.4% and 61.4%, respectively.

To get more in-demand Corolla and Yaris models into the hands of consumers, Toyota will boost production of the two models by a combined 40,000 units in the next three months, Bob Carter, group vice president and general manager-Toyota Div., tells journalists during a conference call to discuss July results.

All three of Toyota’s plants that produce the Corolla, including one in Ontario, the other in California, will see increased production, he says.

Toyota also builds some Corollas in Japan.

“If we had more product in the month of July we would have sold more product in the month of July,” Carter says of Toyota’s fuel-efficient cars.

At Lexus, cars were more to blame for the brand’s July decline, with deliveries slipping 27.2%.

All Lexus car nameplates were down, with the LS flagship off 49.8% from year-ago.

The only Lexus model to post a sales increase was the Land Cruiser-derived LX 570 SUV, new for ’08 and up 277.7%.

And although small cars are hot in the U.S. market right now, sales of Scion’s xB fell 7.5% in July, while the tC coupe continued its long slump, with deliveries down 29.1%.

Toyota Motor Corp. announced earlier this week it expects its U.S. sales to decline about 8% this year to 2.44 million units from 2007’s 2.6 million.